A Zwitterionic Ligand-Based Cationic Metal-Organic Framework for Rapidly Selective Dye Capture and Highly Efficient Cr2O72- Removal

A cationic metal-organic framework (MOF), [Cu2L(H2O)(2)](NO3)(2)5.5H(2)O(1) has been successfully synthesized from a zwitterionic ligand 1,1-bis(3,5-dicarboxyphenyl)-4,4-bipyridinium chlorine ([H4L]Cl-2). The framework of compound 1 contains classical {Cu-2(O2C)(4)} paddlewheels, and possesses typical nbo-type topology and two types of channels with sizes of 5.0 and 15.54 angstrom. Benefitting from the 3D cationic framework and high pore volume, compound1 shows interesting selective adsorption ability for anionic dyes. Such material can be successfully employed in a chromatographic column to efficiently separate mixed dyes of Fluorescein Sodium and Methylene Blue. In addition, compound 1 exhibits excellent Cr2O72- removal capacity with maximum adsorption amount of 222.5mgg(-1), which ranks among the higher Cr2O72- adsorption amounts of MOF materials ever reported, based on ion-exchange. The strategy to construct cationic MOFs based on zwitterionic ligands will promote the development of functional porous materials for the capture and removal of anionic pollutant species from contaminated liquid.